1. Field of the Invention
The present invention relates to an air conditioning system for a vehicle. More particularly, the present invention relates to such a type of air conditioning system for a vehicle, wherein an air flow of low temperature is issued into a cabin of the vehicle from an upper opening of a duct of the system, in such a manner that a thermal load of solar radiation into the cabin is cancelled by the air conditioning system.
2. Description of Related Art
Japanese Unexamined Patent Publication No. 5-131837 discloses an air conditioning system for a vehicle, wherein application of solar radiation to a vehicle causes an increased amount of air flow to be calculated in such a manner that the increase in the thermal load due to the solar radiation is cancelled so as to obtain a corresponding increase in an amount of an air flow issued from an upper outlet of a duct to the cabin at a location corresponding to the face of a driver or a passenger. Furthermore, such an increase in the amount of the air flow issued from the upper opening is obtained as the air flow amount for cancelling the increased load by the solar radiation, multiplied by a weight factor, which has a value varied between 0 to 1.0 in accordance with a difference between a set temperature of the air in the cabin and an actual air temperature in the cabin. Such a multiplication of the varied weight factor can prevent the discharged air flow amount from being excessively increased in case of an existence of a large difference between the set temperature and the actual cabin temperature, which is, for example, obtained during a winter season where the cabin temperature is low, thereby preventing a driver or a passenger from feeling cold. Namely, in winter, a driver or a passenger is less sensitive to the heat of the sun, so that the discharge of a cold air flow from the upper outlet would cause the driver or the passenger to feel cold. In Japanese Unexamined Patent Publication No. 5-131837, an increase in the air flow amount from the upper outlet due to a sun radiation is suppressed when a difference in the cabin temperature between the set value and the actual value is large. However, in this prior art, a reduction in the difference causes the value of the weighting to approach 1.0, so that the value of the air flow increase based on the sun radiation is equal to the value which is obtained when the outside air temperature is high.